<!DOCTYPE html>
<html lang="zh-CN">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width,initial-scale=1">
    <title>理解 AST 实现和编译原理 | 仲灏小栈</title>
    <meta name="generator" content="VuePress 1.9.5">
    <link rel="icon" href="/img/favicon.ico">
    <meta name="description" content="专注web全栈学习与总结。JavaScript,js,ES6,TypeScript,vue,python,css3,html5,Node,git,github等技术文章。">
    <meta name="keywords" content="前端博客,个人技术博客,前端,前端开发,前端框架,web前端,前端面试题,技术文档,学习,面试,JavaScript,js,ES6,TypeScript,vue,python,css3,html5,Node,git,github,markdown">
    <meta name="baidu-site-verification" content="code-5CGlqw1B4p">
    <meta name="google-site-verification" content="PbO8RiLRwDnNwqNFNGnaxZnEFB3CqcGMCGoloYfQXV0">
    <meta name="theme-color" content="#65d1a0">
    
    <link rel="preload" href="/assets/css/0.styles.6c1f7aaa.css" as="style"><link rel="preload" href="/assets/js/app.6d26e8d4.js" as="script"><link rel="preload" href="/assets/js/2.8273876b.js" as="script"><link rel="preload" href="/assets/js/38.2dfd8d32.js" as="script"><link rel="prefetch" href="/assets/js/10.cb095657.js"><link rel="prefetch" href="/assets/js/100.fbcd69a7.js"><link rel="prefetch" href="/assets/js/101.8fad45f8.js"><link rel="prefetch" href="/assets/js/102.16b0b3d1.js"><link rel="prefetch" href="/assets/js/103.c2af4d4a.js"><link rel="prefetch" href="/assets/js/104.d37d4660.js"><link rel="prefetch" href="/assets/js/105.27e54103.js"><link rel="prefetch" href="/assets/js/106.e4098682.js"><link rel="prefetch" href="/assets/js/107.8efeef5d.js"><link rel="prefetch" href="/assets/js/108.6c305bbf.js"><link rel="prefetch" href="/assets/js/109.6f1c6613.js"><link rel="prefetch" href="/assets/js/11.d1f39b42.js"><link rel="prefetch" href="/assets/js/110.6f264ba6.js"><link rel="prefetch" href="/assets/js/111.1b6294ef.js"><link rel="prefetch" href="/assets/js/112.2ad16154.js"><link rel="prefetch" href="/assets/js/113.a40acefc.js"><link rel="prefetch" href="/assets/js/114.d44cb107.js"><link rel="prefetch" href="/assets/js/115.bd15b919.js"><link rel="prefetch" href="/assets/js/116.778a9058.js"><link rel="prefetch" href="/assets/js/117.19ff15b7.js"><link rel="prefetch" href="/assets/js/118.2630ca8d.js"><link rel="prefetch" href="/assets/js/119.604bd439.js"><link rel="prefetch" href="/assets/js/12.892c0d9f.js"><link rel="prefetch" href="/assets/js/120.43a964f8.js"><link rel="prefetch" href="/assets/js/121.5993f55a.js"><link rel="prefetch" href="/assets/js/122.6c054fcf.js"><link rel="prefetch" href="/assets/js/123.95ddd9a3.js"><link rel="prefetch" href="/assets/js/124.c3a9510e.js"><link rel="prefetch" href="/assets/js/125.612c461a.js"><link rel="prefetch" href="/assets/js/126.ccdb194e.js"><link rel="prefetch" href="/assets/js/127.865789a0.js"><link rel="prefetch" href="/assets/js/128.9e0bc723.js"><link rel="prefetch" href="/assets/js/129.68515ee6.js"><link rel="prefetch" href="/assets/js/13.ea744146.js"><link rel="prefetch" href="/assets/js/130.32a31759.js"><link rel="prefetch" href="/assets/js/131.467e7aaf.js"><link rel="prefetch" href="/assets/js/132.3bb05df9.js"><link rel="prefetch" href="/assets/js/133.52bbf931.js"><link rel="prefetch" href="/assets/js/134.ee00e869.js"><link rel="prefetch" href="/assets/js/135.aadd30fb.js"><link rel="prefetch" href="/assets/js/136.6b5bb775.js"><link rel="prefetch" href="/assets/js/137.9d66b052.js"><link rel="prefetch" href="/assets/js/138.1df874a9.js"><link rel="prefetch" href="/assets/js/139.bd1e48e9.js"><link rel="prefetch" href="/assets/js/14.c755eadf.js"><link rel="prefetch" href="/assets/js/140.2a849d58.js"><link rel="prefetch" href="/assets/js/141.28c22cf9.js"><link rel="prefetch" href="/assets/js/142.e99735ee.js"><link rel="prefetch" href="/assets/js/143.0666fdce.js"><link rel="prefetch" href="/assets/js/144.216c1efe.js"><link rel="prefetch" href="/assets/js/145.fad2c93a.js"><link rel="prefetch" href="/assets/js/146.01533714.js"><link rel="prefetch" href="/assets/js/147.1af38e50.js"><link rel="prefetch" href="/assets/js/148.84844c3d.js"><link rel="prefetch" href="/assets/js/149.49ce06ed.js"><link rel="prefetch" href="/assets/js/15.7a29d3f4.js"><link rel="prefetch" href="/assets/js/150.234bdfef.js"><link rel="prefetch" href="/assets/js/151.89e0796a.js"><link rel="prefetch" href="/assets/js/152.389ced87.js"><link rel="prefetch" href="/assets/js/153.07285920.js"><link rel="prefetch" href="/assets/js/154.965fc5c1.js"><link rel="prefetch" href="/assets/js/155.7bf58a9a.js"><link rel="prefetch" href="/assets/js/156.99e400e4.js"><link rel="prefetch" href="/assets/js/157.b6edd5ab.js"><link rel="prefetch" href="/assets/js/158.af656e52.js"><link rel="prefetch" href="/assets/js/159.4b3d37d2.js"><link rel="prefetch" href="/assets/js/16.5c417580.js"><link rel="prefetch" href="/assets/js/160.fa1e9d1b.js"><link rel="prefetch" href="/assets/js/161.43d6f2b4.js"><link rel="prefetch" href="/assets/js/162.c0e7e60f.js"><link rel="prefetch" href="/assets/js/163.c78d27b4.js"><link rel="prefetch" href="/assets/js/164.7ee2986b.js"><link rel="prefetch" href="/assets/js/165.bbc6516b.js"><link rel="prefetch" href="/assets/js/166.90e15253.js"><link rel="prefetch" href="/assets/js/167.18578ca6.js"><link rel="prefetch" href="/assets/js/168.c52ad494.js"><link rel="prefetch" href="/assets/js/169.c34b2d53.js"><link rel="prefetch" href="/assets/js/17.76fdc3b2.js"><link rel="prefetch" href="/assets/js/170.c97f6096.js"><link rel="prefetch" href="/assets/js/171.358f0f02.js"><link rel="prefetch" href="/assets/js/172.30f03133.js"><link rel="prefetch" href="/assets/js/173.b72d5243.js"><link rel="prefetch" href="/assets/js/174.4e333643.js"><link rel="prefetch" href="/assets/js/175.2c07b836.js"><link rel="prefetch" href="/assets/js/176.29bcb24c.js"><link rel="prefetch" href="/assets/js/177.102b3f0f.js"><link rel="prefetch" href="/assets/js/178.5862bde0.js"><link rel="prefetch" href="/assets/js/179.0da54072.js"><link rel="prefetch" href="/assets/js/18.f857e697.js"><link rel="prefetch" href="/assets/js/180.393e8099.js"><link rel="prefetch" href="/assets/js/181.418f9fe8.js"><link rel="prefetch" href="/assets/js/182.e65424fa.js"><link rel="prefetch" href="/assets/js/183.3b3cb092.js"><link rel="prefetch" href="/assets/js/184.73f7a76a.js"><link rel="prefetch" href="/assets/js/185.537623fb.js"><link rel="prefetch" href="/assets/js/186.df802468.js"><link rel="prefetch" href="/assets/js/187.1095bafd.js"><link rel="prefetch" href="/assets/js/188.1d2acd1a.js"><link rel="prefetch" href="/assets/js/189.dc6a5186.js"><link rel="prefetch" href="/assets/js/19.8c1d0f81.js"><link rel="prefetch" href="/assets/js/190.a279b4dd.js"><link rel="prefetch" href="/assets/js/191.3abaa15f.js"><link rel="prefetch" href="/assets/js/192.4d0dd04e.js"><link rel="prefetch" href="/assets/js/193.2c698e6f.js"><link rel="prefetch" href="/assets/js/194.4243beaa.js"><link rel="prefetch" href="/assets/js/195.7c13b124.js"><link rel="prefetch" href="/assets/js/196.b18118bf.js"><link rel="prefetch" href="/assets/js/197.2abfac38.js"><link rel="prefetch" href="/assets/js/198.407f0a8b.js"><link rel="prefetch" href="/assets/js/199.d4e97578.js"><link rel="prefetch" href="/assets/js/20.47831bf7.js"><link rel="prefetch" href="/assets/js/200.86ce407c.js"><link rel="prefetch" href="/assets/js/201.56a65a3f.js"><link rel="prefetch" href="/assets/js/202.f852c6e8.js"><link rel="prefetch" href="/assets/js/203.92530d7a.js"><link rel="prefetch" href="/assets/js/204.ce612269.js"><link rel="prefetch" href="/assets/js/205.b14b2d70.js"><link rel="prefetch" href="/assets/js/206.b5112828.js"><link rel="prefetch" href="/assets/js/207.a4becd8a.js"><link rel="prefetch" href="/assets/js/208.f82e2766.js"><link rel="prefetch" href="/assets/js/209.11566ec8.js"><link rel="prefetch" href="/assets/js/21.8580b0b4.js"><link rel="prefetch" href="/assets/js/210.bf848e0e.js"><link rel="prefetch" href="/assets/js/211.6db52324.js"><link rel="prefetch" href="/assets/js/212.c9a03071.js"><link rel="prefetch" href="/assets/js/213.734c775f.js"><link rel="prefetch" href="/assets/js/214.7654a416.js"><link rel="prefetch" href="/assets/js/215.34ad7e3d.js"><link rel="prefetch" href="/assets/js/216.aabcd184.js"><link rel="prefetch" href="/assets/js/217.26ffe7d6.js"><link rel="prefetch" href="/assets/js/218.d8ceaf2e.js"><link rel="prefetch" href="/assets/js/219.82bad7ef.js"><link rel="prefetch" href="/assets/js/22.2d87ea68.js"><link rel="prefetch" href="/assets/js/220.0c35dcdf.js"><link rel="prefetch" href="/assets/js/221.8657d7c1.js"><link rel="prefetch" href="/assets/js/222.291af8a7.js"><link rel="prefetch" href="/assets/js/223.e8ce5ce0.js"><link rel="prefetch" href="/assets/js/224.2c3c1268.js"><link rel="prefetch" href="/assets/js/225.b31429da.js"><link rel="prefetch" href="/assets/js/226.8ec29e66.js"><link rel="prefetch" href="/assets/js/227.84469b41.js"><link rel="prefetch" href="/assets/js/228.cd6b9967.js"><link rel="prefetch" href="/assets/js/229.e5497c23.js"><link rel="prefetch" href="/assets/js/23.c1a929a6.js"><link rel="prefetch" href="/assets/js/230.643fdbb6.js"><link rel="prefetch" href="/assets/js/231.22457248.js"><link rel="prefetch" href="/assets/js/232.7e94e6f0.js"><link rel="prefetch" href="/assets/js/233.1083085e.js"><link rel="prefetch" href="/assets/js/234.6ce5972b.js"><link rel="prefetch" href="/assets/js/235.bc1d1e7e.js"><link rel="prefetch" href="/assets/js/236.f510d892.js"><link rel="prefetch" href="/assets/js/237.4690c583.js"><link rel="prefetch" href="/assets/js/238.ef69b085.js"><link rel="prefetch" href="/assets/js/239.e7cbaef4.js"><link rel="prefetch" href="/assets/js/24.707a9b9d.js"><link rel="prefetch" href="/assets/js/240.02e1ce4d.js"><link rel="prefetch" href="/assets/js/241.8ccdecd0.js"><link rel="prefetch" href="/assets/js/242.25a5eeac.js"><link rel="prefetch" href="/assets/js/243.80dc6cf3.js"><link rel="prefetch" href="/assets/js/244.d2d264c1.js"><link rel="prefetch" href="/assets/js/245.8646c059.js"><link rel="prefetch" href="/assets/js/246.0d788a8c.js"><link rel="prefetch" href="/assets/js/247.211b425b.js"><link rel="prefetch" href="/assets/js/248.15e5b430.js"><link rel="prefetch" href="/assets/js/249.b28c41d2.js"><link rel="prefetch" href="/assets/js/25.e47a8360.js"><link rel="prefetch" href="/assets/js/250.e4621bbf.js"><link rel="prefetch" href="/assets/js/251.2f49ea1d.js"><link rel="prefetch" href="/assets/js/252.c567824c.js"><link rel="prefetch" href="/assets/js/253.7eb2a6c2.js"><link rel="prefetch" href="/assets/js/254.adf8b2ad.js"><link rel="prefetch" href="/assets/js/255.43d07402.js"><link rel="prefetch" href="/assets/js/256.d49b01ff.js"><link rel="prefetch" href="/assets/js/257.cc61cd1a.js"><link rel="prefetch" href="/assets/js/258.e46ee926.js"><link rel="prefetch" href="/assets/js/259.5c84c742.js"><link rel="prefetch" href="/assets/js/26.db56ba8d.js"><link rel="prefetch" href="/assets/js/260.05cc8cff.js"><link rel="prefetch" href="/assets/js/261.1891f9c6.js"><link rel="prefetch" href="/assets/js/262.0913812a.js"><link rel="prefetch" href="/assets/js/263.a6836819.js"><link rel="prefetch" href="/assets/js/264.363da610.js"><link rel="prefetch" href="/assets/js/265.2cbfbe9f.js"><link rel="prefetch" href="/assets/js/266.555ca792.js"><link rel="prefetch" href="/assets/js/267.83f4c202.js"><link rel="prefetch" href="/assets/js/268.6dea35af.js"><link rel="prefetch" href="/assets/js/269.cbc5306b.js"><link rel="prefetch" href="/assets/js/27.0b0c1f7f.js"><link rel="prefetch" href="/assets/js/270.6bc430c5.js"><link rel="prefetch" href="/assets/js/271.f5105765.js"><link rel="prefetch" href="/assets/js/272.e1541ef7.js"><link rel="prefetch" href="/assets/js/273.158c7593.js"><link rel="prefetch" href="/assets/js/274.efb98c5b.js"><link rel="prefetch" href="/assets/js/275.cf2c3b21.js"><link rel="prefetch" href="/assets/js/276.0bf20a2d.js"><link rel="prefetch" href="/assets/js/277.2e4ddf6c.js"><link rel="prefetch" href="/assets/js/278.7f8b14ac.js"><link rel="prefetch" href="/assets/js/279.83a65d2f.js"><link rel="prefetch" href="/assets/js/28.a5d8ae18.js"><link rel="prefetch" href="/assets/js/280.47de1643.js"><link rel="prefetch" href="/assets/js/281.1d5cab51.js"><link rel="prefetch" href="/assets/js/282.b2299bce.js"><link rel="prefetch" href="/assets/js/283.fdad201b.js"><link rel="prefetch" href="/assets/js/284.cdf83f8f.js"><link rel="prefetch" href="/assets/js/285.caee6eb0.js"><link rel="prefetch" href="/assets/js/286.6b211023.js"><link rel="prefetch" href="/assets/js/287.e9e93db3.js"><link rel="prefetch" href="/assets/js/288.5892d2e1.js"><link rel="prefetch" href="/assets/js/289.48074c49.js"><link rel="prefetch" href="/assets/js/29.0bc8ea25.js"><link rel="prefetch" href="/assets/js/290.b478b2ab.js"><link rel="prefetch" href="/assets/js/291.18239d2b.js"><link rel="prefetch" href="/assets/js/292.9f6b48b4.js"><link rel="prefetch" href="/assets/js/293.70a0b924.js"><link rel="prefetch" href="/assets/js/294.bc5f021a.js"><link rel="prefetch" href="/assets/js/295.dfa72324.js"><link rel="prefetch" href="/assets/js/296.fb717477.js"><link rel="prefetch" href="/assets/js/297.2b2daf25.js"><link rel="prefetch" href="/assets/js/298.0ed3ce25.js"><link rel="prefetch" href="/assets/js/299.c59a3f82.js"><link rel="prefetch" href="/assets/js/3.d68e1d13.js"><link rel="prefetch" href="/assets/js/30.063f8dbe.js"><link rel="prefetch" href="/assets/js/300.f423c130.js"><link rel="prefetch" href="/assets/js/301.a11bcaa5.js"><link rel="prefetch" href="/assets/js/302.5a45b99e.js"><link rel="prefetch" href="/assets/js/303.80ac16da.js"><link rel="prefetch" href="/assets/js/304.f773afc2.js"><link rel="prefetch" href="/assets/js/305.52f1b3ba.js"><link rel="prefetch" href="/assets/js/306.966f2eef.js"><link rel="prefetch" href="/assets/js/307.c22143cf.js"><link rel="prefetch" href="/assets/js/308.a6dfec6e.js"><link rel="prefetch" href="/assets/js/309.377e4f0b.js"><link rel="prefetch" href="/assets/js/31.69d8f2c2.js"><link rel="prefetch" href="/assets/js/310.a76309fc.js"><link rel="prefetch" href="/assets/js/311.0706d5ca.js"><link rel="prefetch" href="/assets/js/312.40513d91.js"><link rel="prefetch" href="/assets/js/313.e36621af.js"><link rel="prefetch" href="/assets/js/314.3d4325be.js"><link rel="prefetch" href="/assets/js/315.72480163.js"><link rel="prefetch" href="/assets/js/316.83f31163.js"><link rel="prefetch" href="/assets/js/317.872fd713.js"><link rel="prefetch" href="/assets/js/318.0dc2aea4.js"><link rel="prefetch" href="/assets/js/319.454e4745.js"><link rel="prefetch" href="/assets/js/32.50aa541b.js"><link rel="prefetch" href="/assets/js/320.d9116236.js"><link rel="prefetch" href="/assets/js/321.b06a7a4e.js"><link rel="prefetch" href="/assets/js/322.41bcaaf1.js"><link rel="prefetch" href="/assets/js/323.f01ba88b.js"><link rel="prefetch" href="/assets/js/324.9a736f30.js"><link rel="prefetch" href="/assets/js/325.49b1193e.js"><link rel="prefetch" href="/assets/js/326.5a07b4a0.js"><link rel="prefetch" href="/assets/js/327.aceece56.js"><link rel="prefetch" href="/assets/js/328.e03489c3.js"><link rel="prefetch" href="/assets/js/329.5673fdef.js"><link rel="prefetch" href="/assets/js/33.4aa00ff3.js"><link rel="prefetch" href="/assets/js/330.246e74fa.js"><link rel="prefetch" href="/assets/js/331.e1cffa6b.js"><link rel="prefetch" href="/assets/js/332.2856b83e.js"><link rel="prefetch" href="/assets/js/333.d4c9c15a.js"><link rel="prefetch" href="/assets/js/334.13b03971.js"><link rel="prefetch" href="/assets/js/335.0b8ed702.js"><link rel="prefetch" href="/assets/js/336.3e71f28d.js"><link rel="prefetch" href="/assets/js/337.f929f08c.js"><link rel="prefetch" href="/assets/js/338.01a6cfbe.js"><link rel="prefetch" href="/assets/js/339.5cd647ad.js"><link rel="prefetch" href="/assets/js/34.b25c4a87.js"><link rel="prefetch" href="/assets/js/340.f941cae0.js"><link rel="prefetch" href="/assets/js/341.aa01a6b1.js"><link rel="prefetch" href="/assets/js/342.edd59a58.js"><link rel="prefetch" href="/assets/js/343.237c716b.js"><link rel="prefetch" href="/assets/js/344.06e59f2b.js"><link rel="prefetch" href="/assets/js/345.ddd4f6fe.js"><link rel="prefetch" href="/assets/js/346.70fe3c42.js"><link rel="prefetch" href="/assets/js/347.d39ad15e.js"><link rel="prefetch" href="/assets/js/348.1b135410.js"><link rel="prefetch" href="/assets/js/349.fd78d783.js"><link rel="prefetch" href="/assets/js/35.a1af8744.js"><link rel="prefetch" href="/assets/js/350.b10e7d69.js"><link rel="prefetch" href="/assets/js/351.a6ae4318.js"><link rel="prefetch" href="/assets/js/352.3117739a.js"><link rel="prefetch" href="/assets/js/353.99e022f1.js"><link rel="prefetch" href="/assets/js/354.a444c2d8.js"><link rel="prefetch" href="/assets/js/355.13d044aa.js"><link rel="prefetch" href="/assets/js/356.d2cfe5d0.js"><link rel="prefetch" href="/assets/js/357.eb44f05f.js"><link rel="prefetch" href="/assets/js/358.394c15db.js"><link rel="prefetch" href="/assets/js/359.6c541551.js"><link rel="prefetch" href="/assets/js/36.5558b717.js"><link rel="prefetch" href="/assets/js/360.65af88d5.js"><link rel="prefetch" href="/assets/js/361.d9b3c889.js"><link rel="prefetch" href="/assets/js/362.37ec0a7d.js"><link rel="prefetch" href="/assets/js/363.49690222.js"><link rel="prefetch" href="/assets/js/364.419b3dab.js"><link rel="prefetch" href="/assets/js/365.1f79df07.js"><link rel="prefetch" href="/assets/js/366.fa710c6f.js"><link rel="prefetch" href="/assets/js/367.497eeda5.js"><link rel="prefetch" href="/assets/js/368.45cf08f6.js"><link rel="prefetch" href="/assets/js/369.80a60b6a.js"><link rel="prefetch" href="/assets/js/37.511798d2.js"><link rel="prefetch" href="/assets/js/370.61b161b4.js"><link rel="prefetch" href="/assets/js/371.545f0249.js"><link rel="prefetch" href="/assets/js/372.d383f896.js"><link rel="prefetch" href="/assets/js/373.df22361b.js"><link rel="prefetch" href="/assets/js/374.0b9872ee.js"><link rel="prefetch" href="/assets/js/375.76bbca97.js"><link rel="prefetch" href="/assets/js/376.1f6f8210.js"><link rel="prefetch" href="/assets/js/377.3dd0dc75.js"><link rel="prefetch" href="/assets/js/378.32cac01d.js"><link rel="prefetch" href="/assets/js/379.6682a524.js"><link rel="prefetch" href="/assets/js/380.1ab9ec1d.js"><link rel="prefetch" href="/assets/js/381.cea4ec7d.js"><link rel="prefetch" href="/assets/js/382.fc51cce1.js"><link rel="prefetch" href="/assets/js/383.489718b4.js"><link rel="prefetch" href="/assets/js/384.a7a1c6d7.js"><link rel="prefetch" href="/assets/js/385.7b2d3a89.js"><link rel="prefetch" href="/assets/js/386.f0a18324.js"><link rel="prefetch" href="/assets/js/387.53063e56.js"><link rel="prefetch" href="/assets/js/388.1115759c.js"><link rel="prefetch" href="/assets/js/389.58bf8aaf.js"><link rel="prefetch" href="/assets/js/39.e8482eab.js"><link rel="prefetch" href="/assets/js/4.de17fbe4.js"><link rel="prefetch" href="/assets/js/40.c6dc3476.js"><link rel="prefetch" href="/assets/js/41.78bfe256.js"><link rel="prefetch" href="/assets/js/42.248cddd4.js"><link rel="prefetch" href="/assets/js/43.6429d3dc.js"><link rel="prefetch" href="/assets/js/44.71e9af05.js"><link rel="prefetch" href="/assets/js/45.f80fb4fc.js"><link rel="prefetch" href="/assets/js/46.3d5e7e58.js"><link rel="prefetch" href="/assets/js/47.1bbf5e9a.js"><link rel="prefetch" href="/assets/js/48.6909050b.js"><link rel="prefetch" href="/assets/js/49.9c775f82.js"><link rel="prefetch" href="/assets/js/5.59910585.js"><link rel="prefetch" href="/assets/js/50.aceb6009.js"><link rel="prefetch" href="/assets/js/51.acd0d321.js"><link rel="prefetch" href="/assets/js/52.a4f9f157.js"><link rel="prefetch" href="/assets/js/53.0f1ec943.js"><link rel="prefetch" href="/assets/js/54.6c5c2837.js"><link rel="prefetch" href="/assets/js/55.f412714f.js"><link rel="prefetch" href="/assets/js/56.64a3862c.js"><link rel="prefetch" href="/assets/js/57.d070eb7d.js"><link rel="prefetch" href="/assets/js/58.a80067c8.js"><link rel="prefetch" href="/assets/js/59.084f5e76.js"><link rel="prefetch" href="/assets/js/6.0ab71a58.js"><link rel="prefetch" href="/assets/js/60.42e0fbb5.js"><link rel="prefetch" href="/assets/js/61.b5b87c23.js"><link rel="prefetch" href="/assets/js/62.014cdbe2.js"><link rel="prefetch" href="/assets/js/63.ff1278d1.js"><link rel="prefetch" href="/assets/js/64.44a86cb2.js"><link rel="prefetch" href="/assets/js/65.1a69bd56.js"><link rel="prefetch" href="/assets/js/66.b8d9a1e9.js"><link rel="prefetch" href="/assets/js/67.48e3c0e6.js"><link rel="prefetch" href="/assets/js/68.127da596.js"><link rel="prefetch" href="/assets/js/69.77e4e1cb.js"><link rel="prefetch" href="/assets/js/7.769e6e3f.js"><link rel="prefetch" href="/assets/js/70.7863bd30.js"><link rel="prefetch" href="/assets/js/71.c5c89c65.js"><link rel="prefetch" href="/assets/js/72.030ac8a4.js"><link rel="prefetch" href="/assets/js/73.e96cf593.js"><link rel="prefetch" href="/assets/js/74.f9319fe7.js"><link rel="prefetch" href="/assets/js/75.049ce9e1.js"><link rel="prefetch" href="/assets/js/76.c71e5605.js"><link rel="prefetch" href="/assets/js/77.1e682453.js"><link rel="prefetch" href="/assets/js/78.0cce7473.js"><link rel="prefetch" href="/assets/js/79.3d32f303.js"><link rel="prefetch" href="/assets/js/8.812618a5.js"><link rel="prefetch" href="/assets/js/80.c956dc30.js"><link rel="prefetch" href="/assets/js/81.8276eaa8.js"><link rel="prefetch" href="/assets/js/82.10f6fdc6.js"><link rel="prefetch" href="/assets/js/83.cac65ec1.js"><link rel="prefetch" href="/assets/js/84.a4ce0ebf.js"><link rel="prefetch" href="/assets/js/85.d9efee67.js"><link rel="prefetch" href="/assets/js/86.cf64260c.js"><link rel="prefetch" href="/assets/js/87.e261e385.js"><link rel="prefetch" href="/assets/js/88.63b9894b.js"><link rel="prefetch" href="/assets/js/89.0ad95e30.js"><link rel="prefetch" href="/assets/js/9.c942e82a.js"><link rel="prefetch" href="/assets/js/90.77f9f729.js"><link rel="prefetch" href="/assets/js/91.3fcbf2d5.js"><link rel="prefetch" href="/assets/js/92.8b57334e.js"><link rel="prefetch" href="/assets/js/93.6095e56a.js"><link rel="prefetch" href="/assets/js/94.c616143f.js"><link rel="prefetch" href="/assets/js/95.a9b61cf9.js"><link rel="prefetch" href="/assets/js/96.a3896e7e.js"><link rel="prefetch" href="/assets/js/97.0318332c.js"><link rel="prefetch" href="/assets/js/98.17b8173b.js"><link rel="prefetch" href="/assets/js/99.d299c156.js">
    <link rel="stylesheet" href="/assets/css/0.styles.6c1f7aaa.css">
  </head>
  <body class="theme-mode-light">
    <div id="app" data-server-rendered="true"><div class="theme-container sidebar-open have-rightmenu have-body-img"><header class="navbar blur"><div title="目录" class="sidebar-button"><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" role="img" viewBox="0 0 448 512" class="icon"><path fill="currentColor" d="M436 124H12c-6.627 0-12-5.373-12-12V80c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12z"></path></svg></div> <a href="/" class="home-link router-link-active"><img src="/img/logo.png" alt="仲灏小栈" class="logo"> <span class="site-name can-hide">仲灏小栈</span></a> <div class="links"><div class="search-box"><input aria-label="Search" autocomplete="off" spellcheck="false" value=""> <!----></div> <nav class="nav-links can-hide"><div class="nav-item"><a href="/" class="nav-link">首页</a></div><div class="nav-item"><a href="/web/" class="nav-link">大前端</a></div><div class="nav-item"><a href="/backend-opt/" class="nav-link">后端&amp;运维</a></div><div class="nav-item"><a href="/other-tech/" class="nav-link">其他技术</a></div><div class="nav-item"><a href="/tech-live/" class="nav-link">生活</a></div><div class="nav-item"><a href="/about/" class="nav-link">关于我</a></div><div class="nav-item"><a href="/favorite/" class="nav-link">收藏</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="索引" class="dropdown-title"><a href="/archives/" class="link-title">索引</a> <span class="title" style="display:none;">索引</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/categories/" class="nav-link">分类</a></li><li class="dropdown-item"><!----> <a href="/tags/" class="nav-link">标签</a></li><li class="dropdown-item"><!----> <a href="/archives/" class="nav-link">归档</a></li></ul></div></div> <a href="https://github.com/izhaong" target="_blank" rel="noopener noreferrer" class="repo-link">
    GitHub
    <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav></div></header> <div class="sidebar-mask"></div> <div class="sidebar-hover-trigger"></div> <aside class="sidebar" style="display:none;"><div class="blogger"><img src="https://cdn.jsdelivr.net/gh/izhaong/izhaong.com-oss/site-data/avatar/avatar-wx.jpg"> <div class="blogger-info"><h3>仲灏</h3> <span>诚意, 正心, 格物, 致知</span></div></div> <nav class="nav-links"><div class="nav-item"><a href="/" class="nav-link">首页</a></div><div class="nav-item"><a href="/web/" class="nav-link">大前端</a></div><div class="nav-item"><a href="/backend-opt/" class="nav-link">后端&amp;运维</a></div><div class="nav-item"><a href="/other-tech/" class="nav-link">其他技术</a></div><div class="nav-item"><a href="/tech-live/" class="nav-link">生活</a></div><div class="nav-item"><a href="/about/" class="nav-link">关于我</a></div><div class="nav-item"><a href="/favorite/" class="nav-link">收藏</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="索引" class="dropdown-title"><a href="/archives/" class="link-title">索引</a> <span class="title" style="display:none;">索引</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/categories/" class="nav-link">分类</a></li><li class="dropdown-item"><!----> <a href="/tags/" class="nav-link">标签</a></li><li class="dropdown-item"><!----> <a href="/archives/" class="nav-link">归档</a></li></ul></div></div> <a href="https://github.com/izhaong" target="_blank" rel="noopener noreferrer" class="repo-link">
    GitHub
    <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav>  <ul class="sidebar-links"><li><a href="/note/infrastructure/" class="sidebar-link">《前端项目基础建设》</a></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>HTML&amp;CSS</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>JavaScript&amp;TypeScript</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/pages/6effaf/" class="sidebar-link">typescript 万金油</a></li><li><a href="/pages/a31c06/" class="sidebar-link">缓缓滚动到顶部实现方式</a></li><li><a href="/pages/9ee936/" class="sidebar-link">js 精准和模糊获取dom</a></li><li><a href="/pages/c466bf/" class="sidebar-link">iframe 笔记</a></li><li><a href="/pages/b3a05e/" class="sidebar-link">文件上传安全问题</a></li><li><a href="/pages/5a1e99/" class="sidebar-link">时间处理</a></li><li><a href="/pages/ea13c1/" class="sidebar-link">Web H5 接入海康录像机 (rtsp转flv)</a></li><li><a href="/pages/9bf063/" class="sidebar-link">全局数据</a></li><li><a href="/pages/b035dd/" class="sidebar-link">持久化数据</a></li><li><a href="/pages/447c40/" class="sidebar-link">typescript 类型库</a></li><li><a href="/pages/963e31/" class="sidebar-link">type</a></li><li><a href="/pages/b19749/" class="sidebar-link">前端开发这些年碰到不常见的api（不论新旧 持续更新）</a></li><li><a href="/pages/a09c96/" class="sidebar-link">js api常用详解</a></li><li><a href="/pages/8b5aea/" class="sidebar-link">搭建typescript环境刷LeetCode算法</a></li><li><a href="/pages/12d678/" class="sidebar-link">typescript 类型联动</a></li><li><a href="/pages/4fff79/" class="sidebar-link">前端避免一直try...catch...(ts装饰器)</a></li><li><a href="/pages/20832d/" class="sidebar-link">高效操作DOM</a></li><li><a href="/pages/e6b2bf/" class="sidebar-link">用好DOM事件</a></li><li><a href="/pages/1c1a0c/" aria-current="page" class="active sidebar-link">理解 AST 实现和编译原理</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/pages/8a752b/" class="sidebar-link">常用正则</a></li><li><a href="/pages/0bc29e/" class="sidebar-link">js面试技能拼图 this</a></li><li><a href="/pages/dd5f5e/" class="sidebar-link">for...in for...of 区别</a></li><li><a href="/pages/8167f9/" class="sidebar-link">js 获取元素大小</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Node</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>构建</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>React</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>小程序</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>跨端</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Electron</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>WebGL&amp;GIS</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>浏览器</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>面经</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>其他</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-06225672><div class="articleInfo" data-v-06225672><ul class="breadcrumbs" data-v-06225672><li data-v-06225672><a href="/" title="首页" class="iconfont icon-home router-link-active" data-v-06225672></a></li> <li data-v-06225672><a href="/web/#大前端" data-v-06225672>大前端</a></li><li data-v-06225672><a href="/web/#JavaScript&amp;TypeScript" data-v-06225672>JavaScript&amp;TypeScript</a></li></ul> <div class="info" data-v-06225672><div title="作者" class="author iconfont icon-touxiang" data-v-06225672><a href="https://github.com/izhaong" target="_blank" title="作者" class="beLink" data-v-06225672>仲灏</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>2023-02-12</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="">理解 AST 实现和编译原理<!----></h1>  <div class="theme-vdoing-content content__default"><p>AST 技术是现代化前端基建和工程化建设的基石：Babel、Webpack、ESLint、代码压缩工具等耳熟能详的工程化基建工具或流程，都离不开 AST 技术；Vue、React 等经典前端框架，也离不开基于 AST 技术的编译。</p> <h3 id="ast-基础知识"><a href="#ast-基础知识" class="header-anchor">#</a> AST 基础知识</h3> <p>先对 AST 下一个定义，AST 是 Abstract Syntax Tree 的缩写，表示抽象语法树：</p> <blockquote><p>在计算机科学中，抽象语法树（Abstract Syntax Tree，AST），或简称语法树（Syntax Tree），是源代码语法结构的一种抽象表示。它以树状的形式表现编程语言的语法结构，树上的每个节点都表示源代码中的一种结构。之所以说语法是“抽象”的，是因为这里的语法并不会表示出真实语法中出现的每个细节。比如，嵌套括号被隐含在树的结构中，并没有以节点的形式呈现；而类似 if-condition-then 这样的条件跳转语句，可以使用带有三个分支的节点来表示。</p></blockquote> <p>AST 的应用场景经常出现在源代码的编译过程中：一般语法分析器创建出 AST，然后 AST 在语义分析阶段添加一些信息，甚至修改 AST 内容，最终产出编译后代码。</p> <h4 id="ast-初体验"><a href="#ast-初体验" class="header-anchor">#</a> AST 初体验</h4> <p>了解了 AST 基本概念，对 AST 进行一个“感官认知”。这里提供给你一个平台：<a href="https://astexplorer.net/" target="_blank" rel="noopener noreferrer">AST explorer<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a>，在这个平台中，可以实时看到 JavaScript 代码转换为 AST 之后的产出结果。如下图所示：</p> <p><img src="https://cdn.jsdelivr.net/gh/izhaong/izhaong.com-oss_2023/blogImg/1020212.%E7%90%86%E8%A7%A3%20AST%20%E5%AE%9E%E7%8E%B0%E5%92%8C%E7%BC%96%E8%AF%91%E5%8E%9F%E7%90%86/2023/02/12/23-44-34-d0f0efbf9319dcd5924c8bb3f828f8b6-Cip5yGAGmb2ABDuIAAE1iKphCso409-70a595.png" alt="Drawing 0.png"></p> <p>AST 在线分析结果图</p> <p>可以看到，经过 AST 转换，的 JavaScript 代码（左侧）变成了一种 ESTree 规范的数据结构（右侧），这种数据结构就是 AST。</p> <p>这个平台实际使用了 <a href="https://github.com/acornjs/acorn" target="_blank" rel="noopener noreferrer">acorn<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> 作为 AST 解析器。</p> <h4 id="acorn-解析"><a href="#acorn-解析" class="header-anchor">#</a> acorn 解析</h4> <p>实际上，社区上多项著名项目都依赖的 acorn 的能力（比如 ESLint、Babel、Vue.js 等），acorn 的介绍为：</p> <blockquote><p>A tiny, fast JavaScript parser, written completely in JavaScript.</p></blockquote> <p>由此可知，acorn 是一个完全使用 JavaScript 实现的、小型且快速的 JavaScript 解析器。基本用法非常简单，代码如下：</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code>let acorn <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token char">'acorn'</span><span class="token punctuation">)</span>
let code <span class="token operator">=</span> <span class="token number">1</span> <span class="token operator">+</span> <span class="token number">2</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>acorn<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span>code<span class="token punctuation">)</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>更多使用方式不再一一列举。你可以结合<a href="https://github.com/acornjs/acorn" target="_blank" rel="noopener noreferrer">相关源码<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a>进一步学习。</p> <p>将视线更多地聚焦 acorn 的内部实现中。对所有语法解析器来说，实现流程上很简单，如下图所示：</p> <p><img src="https://cdn.jsdelivr.net/gh/izhaong/izhaong.com-oss_2023/blogImg/1020212.%E7%90%86%E8%A7%A3%20AST%20%E5%AE%9E%E7%8E%B0%E5%92%8C%E7%BC%96%E8%AF%91%E5%8E%9F%E7%90%86/2023/02/12/23-51-21-8f4427ac8a92a61dbf4da6ddcb9abb27-Cip5yGAGmc2AAm_DAADuYazKZ4U044-6723c3.png" alt="Lark20210119-163409.png"></p> <p>acorn 工作流程图</p> <p>源代码经过词法分析，即分词得到 Token 序列，对 Token 序列进行语法分析，得到最终 AST 结果。但 acorn 稍有不同的是：<strong>acorn 将词法分析和语法分析交替进行，只需要扫描一遍代码即可得到最终 AST 结果</strong>。</p> <p>acorn 的 Parser 类<a href="https://github.com/acornjs/acorn/blob/master/acorn/src/state.js" target="_blank" rel="noopener noreferrer">源码<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a>形如：</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code>export <span class="token keyword">class</span> <span class="token class-name">Parser</span> <span class="token punctuation">{</span>
  <span class="token function">constructor</span><span class="token punctuation">(</span>options<span class="token punctuation">,</span> input<span class="token punctuation">,</span> startPos<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token comment">//...</span>
  <span class="token punctuation">}</span>
  <span class="token function">parse</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token comment">// ...</span>
  <span class="token punctuation">}</span>
  <span class="token comment">// 判断所处 context</span>
  get <span class="token function">inFunction</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">currentVarScope</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>flags <span class="token operator">&amp;</span> <span class="token constant">SCOPE_FUNCTION</span><span class="token punctuation">)</span> <span class="token operator">&gt;</span> <span class="token number">0</span> <span class="token punctuation">}</span>
  get <span class="token function">inGenerator</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">currentVarScope</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>flags <span class="token operator">&amp;</span> <span class="token constant">SCOPE_GENERATOR</span><span class="token punctuation">)</span> <span class="token operator">&gt;</span> <span class="token number">0</span> <span class="token punctuation">}</span>
  get <span class="token function">inAsync</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">currentVarScope</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>flags <span class="token operator">&amp;</span> <span class="token constant">SCOPE_ASYNC</span><span class="token punctuation">)</span> <span class="token operator">&gt;</span> <span class="token number">0</span> <span class="token punctuation">}</span>
  get <span class="token function">allowSuper</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">currentThisScope</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>flags <span class="token operator">&amp;</span> <span class="token constant">SCOPE_SUPER</span><span class="token punctuation">)</span> <span class="token operator">&gt;</span> <span class="token number">0</span> <span class="token punctuation">}</span>
  get <span class="token function">allowDirectSuper</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">currentThisScope</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>flags <span class="token operator">&amp;</span> <span class="token constant">SCOPE_DIRECT_SUPER</span><span class="token punctuation">)</span> <span class="token operator">&gt;</span> <span class="token number">0</span> <span class="token punctuation">}</span>
  get <span class="token function">treatFunctionsAsVar</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">treatFunctionsAsVarInScope</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">currentScope</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
  get <span class="token function">inNonArrowFunction</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">currentThisScope</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>flags <span class="token operator">&amp;</span> <span class="token constant">SCOPE_FUNCTION</span><span class="token punctuation">)</span> <span class="token operator">&gt;</span> <span class="token number">0</span> <span class="token punctuation">}</span>
  <span class="token keyword">static</span> <span class="token function">extend</span><span class="token punctuation">(</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>plugins<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token comment">// ...</span>
  <span class="token punctuation">}</span>
  <span class="token comment">// 解析入口</span>
  <span class="token keyword">static</span> <span class="token function">parse</span><span class="token punctuation">(</span>input<span class="token punctuation">,</span> options<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token keyword">this</span><span class="token punctuation">(</span>options<span class="token punctuation">,</span> input<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">static</span> <span class="token function">parseExpressionAt</span><span class="token punctuation">(</span>input<span class="token punctuation">,</span> pos<span class="token punctuation">,</span> options<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    let parser <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">this</span><span class="token punctuation">(</span>options<span class="token punctuation">,</span> input<span class="token punctuation">,</span> pos<span class="token punctuation">)</span>
    parser<span class="token punctuation">.</span><span class="token function">nextToken</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
    <span class="token keyword">return</span> parser<span class="token punctuation">.</span><span class="token function">parseExpression</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
  <span class="token comment">// 分词入口</span>
  <span class="token keyword">static</span> <span class="token function">tokenizer</span><span class="token punctuation">(</span>input<span class="token punctuation">,</span> options<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token keyword">this</span><span class="token punctuation">(</span>options<span class="token punctuation">,</span> input<span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br></div></div><p>稍做解释：</p> <ul><li>type 表示当前 Token 类型；</li> <li>pos 表示当前 Token 所在源代码中的位置；</li> <li>startNode 方法返回当前 AST 节点；</li> <li>nextToken 方法从源代码中读取下一个 Token；</li> <li>parseTopLevel 方法实现递归向下组装 AST 树。</li></ul> <p>这是 acorn 实现解析 AST 的入口骨架，实际的分词环节主要解决以下问题。</p> <ol><li>明确需要分析哪些 Token 类型。</li></ol> <ul><li>关键字：import，function，return 等</li> <li>变量名称</li> <li>运算符号</li> <li>结束符号</li></ul> <ol><li>状态机：简单来讲就是消费每一个源代码中的字符，对字符意义进行状态机判断。以“对于<code>/</code>的处理”为例，对于<code>3/10</code>的源代码，<code>/</code>就表示一个运算符号；对于<code>var re = /ab+c/</code>源代码来说，<code>/</code>就表示正则运算的起始字符了。</li></ol> <p>在分词过程中，实现者往往使用一个 Context 来表达一个上下文，实际上<strong>Context 是一个栈数据结果</strong>（这一部分源码你可以点击<a href="https://github.com/acornjs/acorn/tree/master/acorn/src" target="_blank" rel="noopener noreferrer">这里<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a>阅读）。</p> <p>acorn 在语法解析阶段主要完成 AST 的封装以及错误抛出。在这个过程中，需要你了解，一段源代码可以用：</p> <ul><li>Program——整个程序</li> <li>Statement——语句</li> <li>Expression——表达式</li></ul> <p>来描述。</p> <p>当然，<strong>Program 包含了多段 Statement，Statement 又由多个 Expression 或者 Statement 组成</strong>。这三种大元素，就构成了遵循 ESTree 规范的 AST。最终的 AST 产出，也是这三种元素的数据结构拼合。具体实现代码不再探究。</p> <p>下面通过 acorn 以及一个脚本，来实现非常简易的 Tree Shaking 能力。</p> <h3 id="ast-实战演练-实现一个简易-tree-shaking-脚本"><a href="#ast-实战演练-实现一个简易-tree-shaking-脚本" class="header-anchor">#</a> AST 实战演练——实现一个简易 Tree Shaking 脚本</h3> <p>实现一个简单的 DCE（dead code elimination）。</p> <p>目标如下，实现一个 Node.js 脚本 treeShaking.js，执行命令：</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code>node treeShaking test<span class="token punctuation">.</span>js
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>可以将<code>test.js</code>中的 dead code 消除。使用<code>test.js</code>测试代码如下：</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code>function <span class="token function">add</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> b<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> a <span class="token operator">+</span> b
<span class="token punctuation">}</span>
function <span class="token function">multiple</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> b<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> a <span class="token operator">*</span> b
<span class="token punctuation">}</span>
<span class="token keyword">var</span> firstOp <span class="token operator">=</span> <span class="token number">9</span>
<span class="token keyword">var</span> secondOp <span class="token operator">=</span> <span class="token number">10</span>
<span class="token function">add</span><span class="token punctuation">(</span>firstOp<span class="token punctuation">,</span> secondOp<span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>理论上讲，上述代码中的<code>multiple</code>方法可以被“摇掉”。</p> <p>进入实现环节，首先请看下图，了解整体架构流程：</p> <p><img src="https://cdn.jsdelivr.net/gh/izhaong/izhaong.com-oss_2023/blogImg/1020212.%E7%90%86%E8%A7%A3%20AST%20%E5%AE%9E%E7%8E%B0%E5%92%8C%E7%BC%96%E8%AF%91%E5%8E%9F%E7%90%86/2023/02/12/23-51-09-9459dce1fb94e03470014b7b6f0813dd-CgqCHmAGmeCARZ9QAAKowCLHfGk667-86c8fb.png" alt="Lark20210119-163411.png"></p> <p>基于 AST 的 tree-shaking 简易实现</p> <p>设计 JSEmitter 类，用于根据 AST 产出 JavaScript 代码（js-emitter.js 文件内容）：</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">class</span> <span class="token class-name">JSEmitter</span> <span class="token punctuation">{</span>
    <span class="token comment">// 访问变量声明，以下都是工具方法</span>
    <span class="token function">visitVariableDeclaration</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> ''
        str <span class="token operator">+=</span> node<span class="token punctuation">.</span>kind <span class="token operator">+</span> <span class="token char">' '</span>
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNodes</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>declarations<span class="token punctuation">)</span>
        <span class="token keyword">return</span> str <span class="token operator">+</span> <span class="token char">'\n'</span>
    <span class="token punctuation">}</span>
    <span class="token function">visitVariableDeclarator</span><span class="token punctuation">(</span>node<span class="token punctuation">,</span> kind<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> ''
        str <span class="token operator">+=</span> kind <span class="token operator">?</span> kind <span class="token operator">+</span> <span class="token char">' '</span> <span class="token operator">:</span> str
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>id<span class="token punctuation">)</span>
        str <span class="token operator">+=</span> <span class="token char">'='</span>
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>init<span class="token punctuation">)</span>
        <span class="token keyword">return</span> str <span class="token operator">+</span> <span class="token char">';'</span> <span class="token operator">+</span> <span class="token char">'\n'</span>
    <span class="token punctuation">}</span>
    <span class="token function">visitIdentifier</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> node<span class="token punctuation">.</span>name
    <span class="token punctuation">}</span>
    <span class="token function">visitLiteral</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> node<span class="token punctuation">.</span>raw
    <span class="token punctuation">}</span>
    <span class="token function">visitBinaryExpression</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> ''
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>left<span class="token punctuation">)</span>
        str <span class="token operator">+=</span> node<span class="token punctuation">.</span>operator
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>right<span class="token punctuation">)</span>
        <span class="token keyword">return</span> str <span class="token operator">+</span> <span class="token char">'\n'</span>
    <span class="token punctuation">}</span>
    <span class="token function">visitFunctionDeclaration</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> 'function '
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>id<span class="token punctuation">)</span>
        str <span class="token operator">+=</span> <span class="token char">'('</span>
        <span class="token keyword">for</span> <span class="token punctuation">(</span>let param <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> param <span class="token operator">&lt;</span> node<span class="token punctuation">.</span>params<span class="token punctuation">.</span>length<span class="token punctuation">;</span> param<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>params<span class="token punctuation">[</span>param<span class="token punctuation">]</span><span class="token punctuation">)</span>
            str <span class="token operator">+=</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>params<span class="token punctuation">[</span>param<span class="token punctuation">]</span> <span class="token operator">==</span> undefined<span class="token punctuation">)</span> <span class="token operator">?</span> '<span class="token char">' : '</span><span class="token punctuation">,</span>'<span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        str <span class="token operator">=</span> str<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> str<span class="token punctuation">.</span>length <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">)</span>
        str <span class="token operator">+=</span> <span class="token char">'){'</span>
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>body<span class="token punctuation">)</span>
        str <span class="token operator">+=</span> <span class="token char">'}'</span>
        <span class="token keyword">return</span> str <span class="token operator">+</span> <span class="token char">'\n'</span>
    <span class="token punctuation">}</span>
    <span class="token function">visitBlockStatement</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> ''
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNodes</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>body<span class="token punctuation">)</span>
        <span class="token keyword">return</span> str
    <span class="token punctuation">}</span>
    <span class="token function">visitCallExpression</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> ''
        <span class="token keyword">const</span> callee <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitIdentifier</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>callee<span class="token punctuation">)</span>
        str <span class="token operator">+=</span> callee <span class="token operator">+</span> <span class="token char">'('</span>
        <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">const</span> arg of node<span class="token punctuation">.</span>arguments<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>arg<span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token char">','</span>
        <span class="token punctuation">}</span>
        str <span class="token operator">=</span> str<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> str<span class="token punctuation">.</span>length <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">)</span>
        str <span class="token operator">+=</span> <span class="token char">');'</span>
        <span class="token keyword">return</span> str <span class="token operator">+</span> <span class="token char">'\n'</span>
    <span class="token punctuation">}</span>
    <span class="token function">visitReturnStatement</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> '<span class="token keyword">return</span> '<span class="token punctuation">;</span>
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>argument<span class="token punctuation">)</span>
        <span class="token keyword">return</span> str <span class="token operator">+</span> <span class="token char">'\n'</span>
    <span class="token punctuation">}</span>
    <span class="token function">visitExpressionStatement</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>expression<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
    <span class="token function">visitNodes</span><span class="token punctuation">(</span>nodes<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> ''
        <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">const</span> node of nodes<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> str
    <span class="token punctuation">}</span>
    <span class="token comment">// 根据类型，执行相关处理函数</span>
    <span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> ''
        <span class="token keyword">switch</span> <span class="token punctuation">(</span>node<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">case</span> '<span class="token class-name">VariableDeclaration</span>'<span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitVariableDeclaration</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
            <span class="token keyword">case</span> '<span class="token class-name">VariableDeclarator</span>'<span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitVariableDeclarator</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
            <span class="token keyword">case</span> '<span class="token class-name">Literal</span>'<span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitLiteral</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
            <span class="token keyword">case</span> '<span class="token class-name">Identifier</span>'<span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitIdentifier</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
            <span class="token keyword">case</span> '<span class="token class-name">BinaryExpression</span>'<span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitBinaryExpression</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
            <span class="token keyword">case</span> '<span class="token class-name">FunctionDeclaration</span>'<span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitFunctionDeclaration</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
            <span class="token keyword">case</span> '<span class="token class-name">BlockStatement</span>'<span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitBlockStatement</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
            <span class="token keyword">case</span> <span class="token string">&quot;CallExpression&quot;</span><span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitCallExpression</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
            <span class="token keyword">case</span> <span class="token string">&quot;ReturnStatement&quot;</span><span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitReturnStatement</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
            <span class="token keyword">case</span> <span class="token string">&quot;ExpressionStatement&quot;</span><span class="token operator">:</span>
                str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitExpressionStatement</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span>
                <span class="token keyword">break</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> str
    <span class="token punctuation">}</span>
    <span class="token comment">// 入口</span>
    <span class="token function">run</span><span class="token punctuation">(</span>body<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        let str <span class="token operator">=</span> ''
        str <span class="token operator">+=</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">visitNodes</span><span class="token punctuation">(</span>body<span class="token punctuation">)</span>
        <span class="token keyword">return</span> str
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword">module</span><span class="token punctuation">.</span><span class="token keyword">exports</span> <span class="token operator">=</span> <span class="token class-name">JSEmitter</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br><span class="line-number">57</span><br><span class="line-number">58</span><br><span class="line-number">59</span><br><span class="line-number">60</span><br><span class="line-number">61</span><br><span class="line-number">62</span><br><span class="line-number">63</span><br><span class="line-number">64</span><br><span class="line-number">65</span><br><span class="line-number">66</span><br><span class="line-number">67</span><br><span class="line-number">68</span><br><span class="line-number">69</span><br><span class="line-number">70</span><br><span class="line-number">71</span><br><span class="line-number">72</span><br><span class="line-number">73</span><br><span class="line-number">74</span><br><span class="line-number">75</span><br><span class="line-number">76</span><br><span class="line-number">77</span><br><span class="line-number">78</span><br><span class="line-number">79</span><br><span class="line-number">80</span><br><span class="line-number">81</span><br><span class="line-number">82</span><br><span class="line-number">83</span><br><span class="line-number">84</span><br><span class="line-number">85</span><br><span class="line-number">86</span><br><span class="line-number">87</span><br><span class="line-number">88</span><br><span class="line-number">89</span><br><span class="line-number">90</span><br><span class="line-number">91</span><br><span class="line-number">92</span><br><span class="line-number">93</span><br><span class="line-number">94</span><br><span class="line-number">95</span><br><span class="line-number">96</span><br><span class="line-number">97</span><br><span class="line-number">98</span><br><span class="line-number">99</span><br><span class="line-number">100</span><br><span class="line-number">101</span><br><span class="line-number">102</span><br><span class="line-number">103</span><br><span class="line-number">104</span><br><span class="line-number">105</span><br><span class="line-number">106</span><br><span class="line-number">107</span><br><span class="line-number">108</span><br><span class="line-number">109</span><br><span class="line-number">110</span><br><span class="line-number">111</span><br><span class="line-number">112</span><br><span class="line-number">113</span><br><span class="line-number">114</span><br><span class="line-number">115</span><br><span class="line-number">116</span><br><span class="line-number">117</span><br><span class="line-number">118</span><br><span class="line-number">119</span><br></div></div><p>来具体分析一下，JSEmitter 类中创建了很多 visitXXX 方法，他们最终都会产出 JavaScript 代码。继续结合<code>treeShaking.js</code>的实现来理解：</p> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">const</span> acorn <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">&quot;acorn&quot;</span><span class="token punctuation">)</span>
<span class="token keyword">const</span> l <span class="token operator">=</span> console<span class="token punctuation">.</span>log
<span class="token keyword">const</span> <span class="token class-name">JSEmitter</span> <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span>'<span class="token punctuation">.</span>/js<span class="token operator">-</span>emitter'<span class="token punctuation">)</span>
<span class="token keyword">const</span> fs <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token char">'fs'</span><span class="token punctuation">)</span>
<span class="token comment">// 获取命令行参数</span>
<span class="token keyword">const</span> args <span class="token operator">=</span> process<span class="token punctuation">.</span>argv<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span>
<span class="token keyword">const</span> buffer <span class="token operator">=</span> fs<span class="token punctuation">.</span><span class="token function">readFileSync</span><span class="token punctuation">(</span>args<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token keyword">const</span> body <span class="token operator">=</span> acorn<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span>buffer<span class="token punctuation">)</span><span class="token punctuation">.</span>body
<span class="token keyword">const</span> jsEmitter <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">JSEmitter</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
let decls <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
let calledDecls <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>
let code <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>
<span class="token comment">// 遍历处理</span>
body<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token function">function</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>node<span class="token punctuation">.</span>type <span class="token operator">==</span> <span class="token string">&quot;FunctionDeclaration&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">const</span> code <span class="token operator">=</span> jsEmitter<span class="token punctuation">.</span><span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">[</span>node<span class="token punctuation">]</span><span class="token punctuation">)</span>
        decls<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>jsEmitter<span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>id<span class="token punctuation">)</span><span class="token punctuation">,</span> code<span class="token punctuation">)</span>
        <span class="token keyword">return</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>node<span class="token punctuation">.</span>type <span class="token operator">==</span> <span class="token string">&quot;ExpressionStatement&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>node<span class="token punctuation">.</span>expression<span class="token punctuation">.</span>type <span class="token operator">==</span> <span class="token string">&quot;CallExpression&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">const</span> callNode <span class="token operator">=</span> node<span class="token punctuation">.</span>expression
            calledDecls<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>jsEmitter<span class="token punctuation">.</span><span class="token function">visitIdentifier</span><span class="token punctuation">(</span>callNode<span class="token punctuation">.</span>callee<span class="token punctuation">)</span><span class="token punctuation">)</span>
            <span class="token keyword">const</span> args <span class="token operator">=</span> callNode<span class="token punctuation">.</span>arguments
            <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">const</span> arg of args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
                <span class="token keyword">if</span> <span class="token punctuation">(</span>arg<span class="token punctuation">.</span>type <span class="token operator">==</span> <span class="token string">&quot;Identifier&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
                    calledDecls<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>jsEmitter<span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>arg<span class="token punctuation">)</span><span class="token punctuation">)</span>
                <span class="token punctuation">}</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>node<span class="token punctuation">.</span>type <span class="token operator">==</span> <span class="token string">&quot;VariableDeclaration&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">const</span> kind <span class="token operator">=</span> node<span class="token punctuation">.</span>kind
        <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">const</span> decl of node<span class="token punctuation">.</span>declarations<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            decls<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>jsEmitter<span class="token punctuation">.</span><span class="token function">visitNode</span><span class="token punctuation">(</span>decl<span class="token punctuation">.</span>id<span class="token punctuation">)</span><span class="token punctuation">,</span> jsEmitter<span class="token punctuation">.</span><span class="token function">visitVariableDeclarator</span><span class="token punctuation">(</span>decl<span class="token punctuation">,</span> kind<span class="token punctuation">)</span><span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span>
    <span class="token punctuation">}</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>node<span class="token punctuation">.</span>type <span class="token operator">==</span> <span class="token string">&quot;Identifier&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        calledDecls<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>node<span class="token punctuation">.</span>name<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
    code<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>jsEmitter<span class="token punctuation">.</span><span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">[</span>node<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 生成 code</span>
code <span class="token operator">=</span> calledDecls<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span>c <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> decls<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>c<span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span><span class="token punctuation">[</span>code<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span>''<span class="token punctuation">)</span>
fs<span class="token punctuation">.</span><span class="token function">writeFileSync</span><span class="token punctuation">(</span>'test<span class="token punctuation">.</span>shaked<span class="token punctuation">.</span>js'<span class="token punctuation">,</span> code<span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br></div></div><p>对于上面代码分析，首先通过<code>process.argv</code>获取到目标文件，对于目标文件通过<code>fs.readFileSync()</code>方法读出字符串形式的内容<code>buffer</code>，对于这个<code>buffer</code>变量，使用<code>acorn.parse</code>进行解析，并对产出内容进行遍历。</p> <p>在遍历过程中，<strong>对于不同的节点类型，调用 JS Emitter 实例不同的处理方法</strong>。在整个过程中，维护了：</p> <ul><li>decls——Map 类型</li> <li>calledDecls——数组类型</li> <li>code——数组类型</li></ul> <p>三个关键变量。<code>decls</code>存储所有的函数或变量声明类型节点，<code>calledDecls</code>则存储了代码中真正使用到的数或变量声明，<code>code</code>存储了其他所有没有被节点类型匹配的 AST 部分。</p> <p>下面来分析具体的遍历过程。</p> <ul><li>在遍历过程中，<strong>对所有函数和变量的声明，都维护到</strong><code>decls</code>中。</li> <li>接着，<strong>对所有的 CallExpression 和 IDentifier 进行检测</strong>。因为 CallExpression 代表了一次函数调用，因此在该 if 条件分支内，将相关函数节点调用情况推入到<code>calledDecls</code>数组中，同时对于该函数的参数变量也推入到<code>calledDecls</code>数组。因为 IDentifier 代表了一个变量的取值，也推入到<code>calledDecls</code>数组。</li></ul> <p>经过整个 AST 遍历，就可以只遍历<code>calledDecls</code>数组，并从<code>decls</code>变量中获取使用到的变量和函数声明，最终使用<code>concat</code>方法合并带入<code>code</code>变量中，使用<code>join</code>方法转化为字符串类型。</p></div></div>  <div class="page-edit"><!----> <!----> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2023/06/10, 12:06:41</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/pages/e6b2bf/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">用好DOM事件</div></a> <a href="/pages/8a752b/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">常用正则</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
        ←
        <a href="/pages/e6b2bf/" class="prev">用好DOM事件</a></span> <span class="next"><a href="/pages/8a752b/">常用正则</a>→
      </span></p></div></div></div> <div class="article-list"><div class="article-title"><a href="/archives/" class="iconfont icon-bi">最近更新</a></div> <div class="article-wrapper"><dl><dd>01</dd> <dt><a href="/pages/e3ef00/"><div>
            接雨水
            <!----></div></a> <span class="date">04-08</span></dt></dl><dl><dd>02</dd> <dt><a href="/pages/a5eeb6/"><div>
            vim日常使用记录
            <!----></div></a> <span class="date">04-08</span></dt></dl><dl><dd>03</dd> <dt><a href="/pages/d46779/"><div>
            有效的字母异位词
            <!----></div></a> <span class="date">04-08</span></dt></dl> <dl><dd></dd> <dt><a href="/archives/" class="more">更多文章&gt;</a></dt></dl></div></div></main></div> <div class="footer"><div class="icons"><a href="mailto:izhaong@outlook.com" title="发邮件" target="_blank" class="iconfont icon-youjian"></a><a href="https://github.com/izhaong" title="GitHub" target="_blank" class="iconfont icon-github"></a><a href="https://music.163.com/#/playlist?id=755597173" title="听音乐" target="_blank" class="iconfont icon-erji"></a></div> 
  Theme by
  <a href="https://github.com/xugaoyi/vuepress-theme-vdoing" target="_blank" title="本站主题">Vdoing</a> 
    | Copyright © 2021-2024
    <span>izhaong | <a href="https://github.com/izhaong" target="_blank">github</a> | <a href="http://beian.miit.gov.cn/" target="_blank">蜀ICP备2021031194号</a></span></div> <div class="buttons"><div title="返回顶部" class="button blur go-to-top iconfont icon-fanhuidingbu" style="display:none;"></div> <div title="去评论" class="button blur go-to-comment iconfont icon-pinglun" style="display:none;"></div> <div title="主题模式" class="button blur theme-mode-but iconfont icon-zhuti"><ul class="select-box" style="display:none;"><li class="iconfont icon-zidong">
          跟随系统
        </li><li class="iconfont icon-rijianmoshi">
          浅色模式
        </li><li class="iconfont icon-yejianmoshi">
          深色模式
        </li><li class="iconfont icon-yuedu">
          阅读模式
        </li></ul></div></div> <div class="body-bg" style="background:url() center center / cover no-repeat;opacity:0.5;"></div> <!----> <!----></div><div class="global-ui"><div></div></div></div>
    <script src="/assets/js/app.6d26e8d4.js" defer></script><script src="/assets/js/2.8273876b.js" defer></script><script src="/assets/js/38.2dfd8d32.js" defer></script>
  </body>
</html>
